A reduction in size and weight has been required of portable communication units typified by portable telephones (cellular phones) from the viewpoint of improving the portability. The reduction in size and weight of the portable communication units is generally realized by reducing the size and weight of components used and, in addition, by reducing the thickness of the body. Reducing the thickness of the body, however, unavoidably leads to lowered strength of the body. Further, reducing the thickness of the body is likely to cause deformation or curving of the body which often causes the depression of a key(s) resulting in erroneous operation, for example, turning-off of power supply, turning-on of power supply, or calling. Various proposals have hitherto been made with a view to solving these problems.
FIG. 1 shows a first example of the conventional portable communication unit disclosed in Japanese Utility Model Laid-Open No. 124897/1987. This portable communication unit aims to reduce the thickness without requiring high strength to the body. In the portable communication unit, a metallic shield plate 102 is disposed on the backside of a printed board 101, and the shield plate 102 and the printed board 101 are fixed to a unit case 103 by a screw 104.
FIG. 2 shows a second example of the conventional portable communication unit disclosed in Japanese Utility Model Laid-Open No. 058829/1991. A mounting substrate 201 is built in a unit body 205, and a switch button 202 is mounted on the mounting substrate 201. An elastic member 204 is interposed between the underside of the switch button 202 and the mounting substrate 201. The switch button 202 comprises a movable part 203a and a fixed part 203b. The fixed part 203b is fixed to the mounting substrate 201. The movable part 203a is provided so as to face the fixed part 203b. The movable part 203a in its bottom periphery is held by the elastic member 204. In the ordinary state, the elastic member 204 functions to separate the movable part 203a from the fixed part 203b. As soon as the movable part 203a is pressed down against the elastic force of the elastic member 204, the switch button 202 is turned on. By virtue of the provision of the elastic member 204, even when the switch button 202 is vibrated as a result of the application of impact to the unit body 205, the elastic member 204 absorbs the load of the switch button 202 and, thus, the erroneous operation of the button switch 202 can be prevented.
Japanese Utility Model Laid-Open No. 9448/1996 discloses a construction wherein a cushioning material such as silicone rubber is provided on the outer surface of a case body. According to this construction, even when the portable telephone has been dropped, the case or the internal mechanism is not broken. Likewise, Japanese Patent Laid-Open No. 331333/1999 discloses a construction wherein a cushioning material is provided between the inner wall of a case and a printed board. According to this construction, deformation caused by the application of a load or an impact to the case is less likely to affect the printed board, and the separation of mounted components or contact failure can be prevented.
Japanese Patent Laid-Open No. 209314/2000 discloses a construction wherein a rib is provided so as to pass through a key operating part and a printed board to permit the printed board and the like to be vertically moved along the rib. According to this construction, even when external force is applied to the case, the printed board and electronic components can be protected against impact and the like. Further, Japanese Patent Laid-Open No. 270063/2000 discloses a construction wherein a reinforcing member is provided along one side of an opening for a liquid crystal display in a front case According to this construction, even when external force is applied to the front case in its portion around the liquid crystal display, damage to the liquid crystal display can be prevented.
The conventional portable communication units, however, have the following drawbacks. Specifically, in the construction disclosed in Japanese Utility Model Laid-Open No. 124897/1987, the use of the metallic shield plate results in increased thickness and weight, and, in addition, the increased number of components leads to an increase in cost. In the construction disclosed in Japanese Utility Model Laid-Open No. 058829/1991, the deformation of the case unavoidably causes erroneous operation of the button switch.
In the construction disclosed in Japanese Utility Model Laid-Open No. 9448/1996, the contemplated effect can be attained in only the portion where the cushioning material is provided. In the construction disclosed in Japanese Patent Laid-Open No. 331333/1999, the use of the cushioning material reduces utilizable space within the unit body, and, thus, the mounting space, which is originally small, is further reduced. The technique disclosed in Japanese Patent Laid-Open No. 209314/2000 can be applied to internally provided printed board and electronic components. This technique, however, cannot be applied to button switches. In the construction disclosed in Japanese Patent Laid-Open No. 270063/2000, the necessity of providing the reinforcing member increases the necessary number of components and, at the same time, reduces mounting space. Further, the effect attained by the provision of the reinforcing member covers only the liquid crystal display.